1. Field of the Invention
The present invention relates to an inspection apparatus which is used for a defect inspection performed during a process of manufacturing an organic electroluminescence element and an electroluminescence element suitable for this defect inspection apparatus.
2. Description of the Related Art
An organic electroluminescence element is a luminescence element having a structure including an organic luminescent layer sandwiched between an anode and a cathode. By applying a voltage, a hole and an electron are injected from an anode and a cathode respectively. An electroluminescence element is an element in which energy generated by recombining the pair of the hole and the electron on the surface of an organic electroluminescence layer or within an organic electroluminescence layer is emitted as light. Although an organic electroluminescence element using an organic substance for a luminescent layer had been researched since long ago, there was no progress of a practical application due to problems of low luminescent efficiency. Whereas, an organic electroluminescence element having a laminated structure in which an organic layer was divided into two layers composed of a luminescent layer and a hole transport layer was proposed by C. W. Tang in 1987. Then, luminescence of high efficiency was confirmed under the condition of a low voltage (referred to as non-patent literature 1). Since that time, organic electroluminescence elements have been actively researched.
Organic materials used for a luminescent layer of an organic electroluminescence element are divided into a low molecular material and a high molecular material. A method of forming a luminescent layer varies according to the materials. For a low molecular material, a method for forming a film by an evaporation method is mainly used. For a high molecular material, a method for applying the high molecular material being dissolved or dispersed in a solvent on a substrate is used. And to make an organic electroluminescence element full colored, a luminescent layer is patterned. In the above patterning method, for a low molecular material, a method of evaporating and forming a luminescent material of different luminescent colors on a part corresponding to an intended picture element is performed and the method uses a mask on which a pattern corresponding to an intended picture element shape is formed. The above method is superior when a thin layer is evenly formed on an intended shape. However, a problem is that it becomes difficult to form a pattern in terms of accuracy of a mask when an evaporated substrate is large.
On the other hand, for a high molecular material, a pattern formation by an ink jet method and a pattern formation method by printing are mostly used. For example, an ink jet method disclosed in Japanese Patent Laid-Open No. H 10-12377 Official Gazette is the method of discharging a luminescent layer material dissolved in a solvent on a substrate from an ink jet nozzle and drying a luminescent layer material on the substrate to provide an intended pattern. However, since an ink droplet discharged from a nozzle is spherical, when the ink droplet drops onto the substrate, the ink spreads in a circular shape. Therefore, the shape of the pattern which is formed lacks linearity. In another case, since the accuracy of the point where the ink droplet is dropped is poor, there is a problem in that a linear pattern can not be obtained. On the other hand, for example, in Japanese Patent Laid-Open No. 2002-305077 Official Gazette, a method for forming a linear pattern by the following processes is disclosed: a bank having an ink-repellent property is formed on a substrate by a photolithography method or the like; thereafter, an ink droplet is dropped on the substrate and the ink is repelled according to the shape of the bank and a linear pattern is formed. However, when the repelled ink returns inside a picture element, the ink builds up. Thereby there remains a problem in that a fluctuation of film thickness of an organic luminescent layer inside a picture element occurs.
Then, an ink is made by using an organic high molecular luminescent material which is dissolved or dispersed in a solvent, instead of a low molecular organic luminescent material. A method for forming a pattern by a printing method using the ink has been proposed. In particular, a method performed by relief printing, a method performed by reverse type printing and a method performed by screen printing have been proposed. Especially, relief printing is superior in terms of accuracy of pattern formation and evenness of film thickness. Thereby, relief printing is suitable for a method for manufacturing an organic electroluminescence element performed by a printing method.
In the case of a pattern formation by a wet process such as an ink jet method and printing method, a process of forming a luminescent layer by patterning ink on a substrate is generally performed in air or in a nitrogen atmosphere. After this, ink is dried and a cathode is vacuum-evaporated by a vaporizing apparatus. Moreover, in the case of a top emission type element, an electrode can be made by sputtering instead of a vaporizing apparatus. And after a substrate undergoes a process of sealing and trimming, it becomes possible to activate and illuminate a panel by mounting a driving circuit.
However, when some failure occurs under a process of forming an organic luminescent layer and there is a defect in a pattern, until a driving circuit is attached and luminescence is confirmed, the failure is unperceivable. Furthermore, there is a case that a failure occurs continuously in all patterns of a formed luminescent layer depending on the content of a failure. In this case, in other words, at the stage where a defect in a panel is recognized, the substrates which underwent a process of forming an organic luminescent layer pattern after a substrate having a defect had undergone the process have all had a failure and loss of these substrates is a large problem.
As a solution to this problem, a manufacturing method in which a process loss is decreased is disclosed in Patent Document 1 JP-A-2001-291585. The method is as follows: an inspection is performed in a vacuum condition or a dried atmosphere between a process of evaporating an organic layer and an electrode on a substrate and a sealing process; and a defect can be discovered promptly. And in Patent Document 2 JP-A-2007-12357, a manufacturing method in which a process loss is decreased is disclosed as follows: the previous process is controlled by defect information taken after completion of a forming process by a roll to roll method, using an uninterrupted sheet-shaped substrate; with the above method, an additional process upon a defect generation point is omitted.
Clogging and a blot of a nozzle in an ink jet method and a blot of a plate, an anilox roll and a doctor blade in a printing method are examples of a continuously occurring failure. Thereby, after a luminescent layer is formed on a substrate, a defect inspection of a luminescent layer pattern on a substrate is performed as soon as possible and it is preferable that continuous generation of a defective substrate is prevented.
An optical inspection is performed broadly as an inspection method of a pattern formed on a substrate. An optical inspection determines whether a pattern formation is good or not by the following method: A pattern image on a substrate is taken in by a camera or a line sensor and next an image enhancement and a defect determination is performed. As a method of extracting a defect, an inspection method called die to die comparison, a method for practicing a contour definition and a method for practicing a comparison with an adjacent pattern are used. Among the above, a method for comparing with an adjacent pattern is suitable for an inspection of a substrate on which the same pattern lies regularly. And this method is used as a picture element defect inspection apparatus of a flat-panel display.
The light intensity of ultraviolet rays with which an inspection object of an interlevel product of an organic electroluminescence layer is irradiated to obtain an image is minimized. Therefore, degradation of an organic electroluminescence layer caused by an accumulative irradiance volume of ultraviolet lays generated at the time of an inspection is prevented. The above inspection method is disclosed in Patent document 3. However, a material used for an organic luminescent layer is very weak with an ultraviolet radiation and visible light under an oxygen presence. Then, a material is degraded by light irradiation. Therefore, even if an organic electroluminescence element is formed, a reduction in efficiency and lifetime occurs. Therefore, an optical inspection as shown in the above described method is not preferable.
Moreover, after a luminescent layer pattern is formed, a process of forming an electrode (a cathode) is performed by a vacuum process as shown above. Thereby, performing an optical inspection to avoid light irradiation in air is also possible after injecting a substrate into a vacuum chamber. However, in general, to make it possible that an optical effect inspection apparatus brings in an image of the whole surface of a substrate with one scan or a return scan to reduce inspection time, multiple cameras according to the size of the substrate, resolution and camera view are arranged in a line. Therefore, the apparatus required is large scale. Therefore, the dimensions of a vacuum chamber have to be large to install this defect inspection apparatus. Therefore, the optical defect inspection apparatus is not preferable, because the entire apparatus is expensive, including vacuum evacuation.
The present invention gave consideration to the above circumstances and a purpose of the present invention is to provide a defect inspection apparatus which performs a defect inspection of a luminescent layer pattern on a substrate as soon as possible after a luminescent layer is formed on the substrate, detects a substrate having a defect in a pattern formation by detecting a pattern defect of a luminescent layer and can improve productive efficiency. And the above are performed during a process of manufacturing an organic electroluminescence element. In addition, the purpose of the present invention is to provide an organic electroluminescence element suitable for the defect inspection apparatus.    [Patent Document1] JP-A-2001-291585    [Patent Document2] JP-A-2007-12357    [Patent Document3] JP-A-2006-329819    [Non-patent Document1]C. W. Tang, S. A. VanSlyke, Applied Physics Letters, Vol. 51, Page. 913, 1987.